In order to lower the cost of communications, it has become desirable to increase data rate and the number of communication channels available for such communications. This is particularly true in fiber optic communication systems.
In fiber optic communication systems, wavelength division multiplexing (WDM) has been used over the same fiber optic communication link so that multiple channels of communication may be established over the same optical link. The multiple channels of communication are established at different center wavelengths of light. However, at high data transmission rates, fiber dispersion distorts the optical signal, which adversely affects reliability for correctly recovering data over long distance data transmissions.
In particular, for direct detect systems, fiber dispersion manifests itself as channel nulls in the power spectral density (PSD) of the transmitted signal. These “channel nulls” are substantial reductions in energy that may distort the perceived content within the signal. As optical communication links increase in distance, more channel nulls are experienced. In other words, optical signals experience more distortion as they travel over a longer optical communication link. For instance, 2-3 channel nulls may be experienced when the optical communication link is approximately two-hundred kilometers (200 Km) in length. However, approximately seven (7) channel nulls may be experienced when the optical communication link is approximately six-hundred kilometers (600 Km).
Hence, removal or mitigation of distortion experienced on these long-haul (single-mode) optical communication links would improve the operations of a network, especially for upcoming technologies where the optical fiber communication links are operating at bit rates greatly exceeding 10 gigabits per second such as 100 gigabits per second (100 Gbps) or more.